Laws Promoting Influenza Vaccination Within Hospitals Reduces Flu Cases

Mariana Carrera, PhD

While the US Centers for Disease Control and Prevention (CDC) recommends vaccinating health care workers for influenza, the impact of these laws on pneumonia and influenza mortality has not been identified.

A team, led by Mariana Carrera, PhD, Montana State University, measured the effect of state-level hospital worker influenza vaccination laws on pneumonia and influenza mortality.

Beginning in 1995, 14 states have enacted laws either encouraging or mandating influenza vaccinations for hospital workers.

Comparing Adopting and Non-Adopting States

In the quasi-experimental observational study, investigators examined population level data from all states between 1995-2017. The research team measured pneumonia and influenza mortality per 100,000 persons by state and by month.

The analysis was done both population-wide and separately by age group, using data obtained from restricted-access National Vital Statistics System files.

They then used linear and log-linear models to compare changes in mortality rates for adopting compared to non-adopting states.

The results show state laws mandating hospitals offer influenza vaccination for hospital employees was linked to a 2.5% reduction in the monthly pneumonia and influenza mortality rate (-0.16 deaths per 100,000 individuals; 95% CI, -0.29 to -0.02; P = 0.022) during the years when the influenza vaccine was well matched to the predominant circulating strains.

The largest benefits occurred in the elderly population and during peak influenza months.

Future Studies Still Needed

The investigators also said the utilization of national data did not allow them to analyze more specific outcomes, including laboratory-confirmed or hospital-acquired influenza.

“State laws promoting hospital worker vaccination against influenza may be effective in preventing pneumonia- and influenza-related deaths, particularly among elderly persons,” the authors wrote. “Vaccinating hospital workers may substantially reduce the spread of influenza and protect the most vulnerable populations.”

Influenza Vaccine Reduces COVID-19 Severity

Recently, investigators found the flu vaccine could in fact reduce the severity of coronavirus disease 2019 (COVID-19) infections.

In a new study comparing outcomes of patients hospitalized for COVID-19 who did or did not receive influenza vaccination prior to hospitalization, investigators from the University of Basel and the Swiss Tropical and Public Health Institute identified over 53,000 patients hospitalized for COVID-19 in Brazil between January 1 and June 23, 2020 from the country's national electronic respiratory infection data system, distinguishing patients who had received inactivated trivalent influenza vaccination.

The investigators reported that mortality was consistently lower across all age groups of patients receiving vaccination in March 2020 or later, with absolute mortality differences ranging from a risk difference of 12% in patients 10-19 years of age to 3% in the very elderly patients ≥90 years old. The putative-protective association was not found in those vaccinated earlier, or in 2019.

Overall, influenza vaccination received in 2020 and prior to onset of COVID-19 pandemic was associated with 17% lower odds of mortality, and with 36% lower odd of mortality if administered after onset of clinical COVID-19 symptoms.

The investigators characterize this finding as "surprising," but note the 2 estimates were not statistically significantly different given the numbers of patients in those groups.

The study, “Population Mortality and Laws Encouraging Influenza Vaccination for Hospital Workers,” was published online in the Annals of Internal Medicine.